Circuit board structure and method for fabricating the same

ABSTRACT

A circuit board structure and a method for fabricating the same are proposed. A plurality of conductive bumps and a first solder mask are formed on a carrier board, and the first solder mask is filled in the gaps between the conductive bumps and the conductive bumps are exposed. A first circuit layer and a first heat sink are formed on the first solder mask and the conductive bumps. A second heat sink is formed on the first heat sink, and a dielectric layer is formed on the first circuit layer and the first solder mask except the first and second heat sinks. A second circuit layer is formed on the dielectric layer and is electrically conductive to the first circuit layer. A third heat sink is formed on the second heat sink and a heat sink used for a chip mounting thereon is embedded in the dielectric layer. Therefore, the dimension of the circuit board is reduced and it is conformed to the dimension minimization progress of electronic devices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a circuit board structure and a method for fabricating the same, and more particularly, to a circuit board structure integrated with heat sinks and a method for fabricating the same.

2. Description of Related Art

With the rapid development of electronic industry, modern electronic products have various functions and better performance. In order to meet the requirements of small dimension but high integration for a semiconductor chip, a circuit board, which is used for carrying a plurality of active and passive components, is changed from having only one layer to having multiple layers.

However, such a small-dimensiond but highly integrated semiconductor chip generates considerate amount of heat, which easily overheats or even makes unrecoverable damage on the semiconductor chip

Adhering a plurality of heat dissipating spreaders onto the circuit board is one of the most popular ways to dissipate the heat generated by the semiconductor chip. Please refer to FIG. 1, which is a cross sectional view of a cavity-down ball grid array (CDBGA) package structure 10 according to the prior art. The package structure comprises a circuit board 11, a cavity 113 formed on the circuit board 11, a heat dissipating spreader 12 adhered to a first surface 11 a of the circuit board 11, a semiconductor chip 13 held in the cavity 113 and on the heat dissipating spreader 12. The heat dissipating spreader 12 comprises a high heat conductivity material such as copper. The semiconductor chip 13 comprises an active surface 13 a and an inactive surface 13 b. In a process to assembly the package structure 10, the semiconductor chip 13 is disposed in the cavity 113 of the circuit board 11, a non-electrically active surface 13 b is adhered to the heat dissipating spreader 12, a plurality of solder pads 17 are disposed on a second surface 11 b of the circuit board 11, a plurality of arc solder wires 14 are formed by a solder wire process to electrically connect the semiconductor chip 13 to a plurality of electrically conductive pads 114 disposed on the second surface 11 b of the circuit board 11, an encapsulant 15 is formed by an encapsulant process to covering the semiconductor chip 13 and the arc solder wires 14, and a plurality of solder balls 16 are implanted by a ball implanting process on the second surface 11 b of the circuit board 11.

Although the heat dissipating spreader 12 can effectively dissipate heat generated by the semiconductor chip 13, the solder balls 16 have to be disposed higher than the arc solder wires 14 to ensure the solder balls can be soldered to the external electronic device such as a printed circuit board, this affecting a layout of the circuit board 11. Moreover, the arc solder wires near the semiconductor chip 13 are crowded and easily short to each other. Further, in the encapsulant process, the circuit board 11, on which the semiconductor chip 13 and the arc solder wires 14 are already disposed, is placed in a package mold, and then epoxy resin is injected into the mold to form the encapsulant 15 for covering the semiconductor chip 13 and the arc solder wires 14. However, the semiconductor chip 13 generally does not fit the mold and will not be fixed in the mold tightly and closely, so the epoxy resin is easily injected to a region outside of the mold and part of the encapsulant 15 are formed on the second surface 11 b of the circuit board 11. In result, the package structure 10 is uneven and looks untidy and some of the solder pads 17 may get contaminated, affecting the electrical conductive quality of the package structure 10 because the contaminated solder pads 17 and the solder balls 16 thereon can not be conductive tightly. Moreover, the epoxy resin a kind of fluid, and affects the electrical conductive between the semiconductor chip 13 and the circuit board 11 when injected into the mold. If the epoxy resin is injected excessively in terms of quantity and speed into the mold, the arc solder wires 16 will be drawn too close or even contact to each other, resulting in a short problem and degrading the package structure 10.

Moreover, adhering the heat dissipating spreader 12 onto the circuit board 11 increases the thickness of the package structure 10, which is contradictory to a development trend that a modern electronic device is required to have varieties of functions and compact dimension.

Therefore, how to provide a circuit board structure having well heat dissipating capability, to solve the drawbacks of the prior art that the package structure 10 has too big the dimension because the heat dissipating spreader 12 is adhered to the circuit board 11, has becoming one of the urgent errands in the art.

SUMMARY OF THE INVENTION

In views of the above-mentioned problems of the prior art, it is a primary objective of the present invention to provide a circuit board structure and a method fabrication the same, for providing a chip disposed on the circuit board structure a well heat dissipating path and reducing the dimension of a circuit board.

To achieve the above-mentioned and other objectives, a circuit board structure and a method for fabricating the same are provided according to the present invention. The method includes forming on a carrier board a plurality of conductive bumps and first solder masks filled in gaps between the conductive bumps for exposing the conductive bumps; forming on the first solder masks and the conductive bumps a conductive layer and on the conductive layer a first resistive layer having a plurality of openings for exposing part of the conductive layer; forming in the openings of the first resistive layer a first circuit layer and a first heat sink; forming on the first heat sink, the first resistive layer and the first circuit layer a second resistive layer having a plurality of openings for exposing the first heat sink; forming a second heat sink on the first heat sink exposed to a region outside of the openings of the second resistive layer; removing the second resistive layer, the first resistive layer and the conductive layer covered by the first resistive layer, and forming a dielectric layer on the first circuit layer and the first solder mask where neither the first heat sink nor the second heat sink is formed; and forming on the second heat sink a third heat sink, and forming on the dielectric layer a second circuit layer electrically conductive to the first circuit layer.

The method further includes removing the carrier board. The method further includes forming on the second circuit layer a second solder mask having a plurality of openings for exposing an electrically conductive pads of the second circuit layer. The method further includes performing a circuit build-up process on the second circuit layer to form a circuit build-up structure.

The circuit board structure fabricated by the method includes a dielectric layer having a first surface and a second surface; a plurality of heat sinks embedded in the dielectric layer and protruding to a region above the second surface of the dielectric layer; a first circuit layer embedded in the dielectric layer and disposed evenly with the first surface of the dielectric layer; and a second circuit layer formed on the second surface of the dielectric layer second surface and electrically conductive to the first circuit layer, wherein the first circuit layer is electrically conductive by a conductive via formed in the dielectric layer to the second circuit layer.

The circuit board structure further includes a first solder mask formed on the first surface of the dielectric layer and having a plurality of openings for exposing part of the first circuit layer, a plurality of conductive bumps formed in the openings of the first solder mask, and a second solder mask formed on the second circuit layer and having a pluralities of openings for exposing the electrically conductive pads of the second circuit layer.

Compared with the prior art, the circuit board structure and the method for fabricating the same integrate the heat sinks directly into the circuit board, which already has the first circuit layer, the dielectric layer and the second circuit layer. Therefore, the circuit board of the present invention is thin and can be applied to a modern electronic device required to be minimization.

Moreover, embedded with heat sinks, the circuit board needs not to reserve a certain space for the installation of the heat sinks and has a larger circuit layout space, so as to overcome the drawback of the prior art that the circuit board does not have a big layer space because a certain space on the circuit board has to be reserved for a heat dissipating spreader ready to be adhered to the circuit board.

Further, in the present invention the heat sinks are integrated into the circuit board to for a circuit board structure having well heat dissipating capability, such that heat dissipated by a semiconductor chip disposed on the heat sinks can be conducted over the heat sinks. A circuit build-up layer can be further formed on the circuit board structure of the present invention, so as to form a multi-layered circuit structure.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein:

FIG. 1 is a cross sectional view of a cavity-down ball grid array (CDBGA) package structure 10 according to the prior art;

FIG. 2A-2J are ten cross sectional views demonstrating a method for fabricating a circuit board structure of a first embodiment according to the present invention; and

FIGS. 3A and 3B are two cross sectional views demonstrating a method for fabricating a circuit board structure of a second embodiment according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following illustrative embodiments are provided to illustrate the disclosure of the present invention, these and other advantages and effects can be apparently understood by those in the art after reading the disclosure of this specification. The present invention can also be performed or applied by other different embodiments. The details of the specification may be on the basis of different points and applications, and numerous modifications and variations can be devised without departing from the spirit of the present invention.

FIGS. 2A to 2J are ten cross sectional views demonstrating a method for fabricating a circuit board structure of a first embodiment according to the present invention.

As shown in FIG. 2A, the method comprises providing a carrier board 20, and forming a plurality of conductive bumps 21 on the carrier board 20 by first forming on the carrier board 20 a resistive layer having a plurality of openings for exposure of the carrier board 20, then forming the conductive bumps 21 on the carrier board 20 where the openings are formed, and finally removing the resistive layer. The conductive bumps 21 are used for connecting to an external electronic device. According to the first embodiment, at least one of the conductive bumps 21 comprises solder tin, the carrier board 20 is a metal board, and the conductive bumps 21 are electroplated on the carrier board 21.

The method further comprises forming a first solder mask 22 in gaps between the conductive bumps 21.

As shown in FIG. 2B, the method further comprises forming on the first solder mask 22 and the conductive bumps 21 a conductive layer 23, which is used as a current conductive path needed by an electroplated metal material subsequently formed on the circuit board structure. According to the first embodiment, the conductive layer 23 comprises metal, alloy, a couple of deposited metal or a conductive polymer material.

As shown in FIG. 2C, the method further comprises forming on the conductive layer 23 a first resistive layer 24 for covering part of the conductive layer 23 and exposing a plurality of openings 240 reserved for the formation of a plurality of circuit layers and heat sinks formed by an electroplating process. According to the first embodiment, the first resistive layer 24 is a photoresist layer, such as a liquid photoresist layer and a dry film layer, and formed on the conductive layer 23 by printing, spin-coating or adhering techniques and exposing and developing processes.

As shown in FIG. 2D, the method further comprises performing the electroplating process on the conductive layer 23, which is conductive and serves as the current conductive path, to form a first circuit layer 25 and a first heat sink 251 in the openings 240.

As shown in FIG. 2E, the method further comprises forming on the first heat sink 251, the first resistive layer 24 and the first circuit layer 25 a second resistive layer 26 having a plurality of openings 260 for exposing the first heat sink 251 of the first circuit layer 25. According to the first embodiment, the second resistive layer 26 is also a photoresist layer, such as the liquid photoresist layer and the dry film layer, and formed on the first resistive layer 24 and the first circuit layer 25 by the printing, spin-coating or adhering techniques and the exposing and developing processes. The method further comprises performing the electroplating process on the first heat sink 251 exposed from the openings 260 of the second resistive layer 26 to form a second heat sink 252.

As shown in FIG. 2F, the method further comprises removing the second resistive layer 26, the first resistive layer 24 and the conductive layer 23, which is originally covered by the first resistive layer 24.

As shown in FIG. 2G, the method further comprises forming a dielectric layer 28 on the first circuit layer 25 and the first solder mask 22 where neither the first heat sink 251 nor the second heat sink 252 is disposed, and forming a via 280 on the dielectric layer 28 by laser drilling, plasma etching or mechanically drilling techniques for exposing part of the first circuit layer 25. According to the first embodiment, the dielectric layer 28 comprises FR-4 resin, FR-5 resin, epoxy resin, polyesters resin, cyanate ester, polyimide, bismaleimide Triazine (BT) or insulating materials, such as mixed epoxy resin and glass fiber.

As shown in FIG. 2H, the method further comprises forming on the dielectric layer 28, the second heat sink 252 and the via 280 a conductive layer 29, which is used as another current conductive path needed by an electroplated metal material subsequently form on the circuit board structure. According to the first embodiment, the conductive layer 29 comprises metal, alloy, a couple of deposited metal or a conductive polymer material.

The method further comprises forming on the conductive layer 29 a pattered third resistive layer 30 for covering part of the conductive layer 29. According to the first embodiment, the third resistive layer 30 is a photoresist layer, such as a liquid photoresist layer and a dry film layer, and formed on the conductive layer 29 by printing, spin-coating or adhering techniques and exposing and developing processes. Therefore, a plurality of openings 300 reserved for the formation of a plurality of circuit layers and heat sinks are formed on the third resistive layer 30. At least one of the openings 300 is corresponding in position to the second heat sink 252.

As shown in FIG. 21, through the use of the conductive layer 29, which is conductive and serves as the current conductive path, the method further comprises performing the electroplating process on the openings 300 of the third resistive layer 30 as previous description to form a third heat sink 253, a conductive via 280 a and a second circuit layer 31, which is conductive via the conductive via 280 a to the first circuit layer 25. The method further comprises removing the third resistive layer 30 and the conductive layer 29 covered thereby.

As shown in FIG. 2J, the method further comprises forming on the second circuit layer 31 a second solder mask 32 having a plurality of openings 320 for exposing the third heat sink 253 and an electrically conductive pad 311 of the second circuit layer 31. The method further comprises forming a metal protection layer such as a nickel/gold layer, and removing the carrier board 20, so as to form the circuit board structure, which is embedded with heat sinks.

The circuit board structure fabricated by the method demonstrated in the first embodiment comprises the dielectric layer 28 having a first surface 28 a and a second surface 28 b, a plurality of stacked heat sinks embedded in the dielectric layer 28 and exposed to the second surface 28 b of the dielectric layer 28, the first circuit layer 25 embedded in the dielectric layer 28 and disposed evenly with the first surface 28 a of the dielectric layer 28, and the second circuit layer 31 formed on the second surface 28 b of the dielectric layer 28 and electrically conductive to the first circuit layer 25. The first circuit layer 25 is electrically conductive by the conductive via 280 a formed in the dielectric layer 28 to the second circuit layer 31. The stacked heat sinks include the first heat sink 251 and the second heat sink 252 embedded in the dielectric layer 28, and third heat sink 253 exposed to the second surface 28 b of the dielectric layer.

The first surface 28 a of the dielectric layer 28 is covered by the first solder mask 22. The first solder mask 22 has the openings 22 a for exposing part of the first circuit layer 25 and the first heat sink 251. The conductive bumps 21 are formed in the openings 22 a of the first solder mask 22 and is disposed evenly with the first solder mask 22. At least one of the conductive bumps 21 comprises a metal material such as solder tin. Both the second surface 28 b of the dielectric layer 28 and the second circuit layer 31 are covered by the second solder mask 32, which has the openings 320 for exposing the third heat sink 253 and part of the second circuit layer 31 as the electrically conductive pad 311. The metal protection layer such as the nickel/gold layer is covered on the third heat sink 253 and the second circuit layer 31 where the second solder mask 32 is not disposed.

Please refer to FIGS. 3A and 3B, which are another two cross sectional views demonstrating another method for fabricating a circuit board structure of a second embodiment according to the present invention. Compared with the method demonstrated in the first embodiment, the method demonstrated in the second embodiment further comprises performing a circuit build-up process on the second circuit layer 31.

As shown in FIG. 3A, the method further comprises performing the circuit build-up process on the second circuit layer 31 and the third heat sink 253 of the circuit board structure fabricated by the method demonstrated in the first embodiment and already having the first circuit layer 25, the second circuit layer 31, the first heat sink 251, the second heat sink 252, the third heat sink 253, the dielectric layer 28, the first solder mask 22 and the conductive bumps 21 (referring to FIG. 21), to form on the second circuit layer 31 a circuit build-up structure 34 electrically conductive to the second circuit layer 31, and increasing the thickness of the heat sinks to form a fourth heat sink 254 on the third heat sink 253.

The circuit build-up structure 34 comprises a dielectric layer 340, a circuit layer 342 stacked on the dielectric layer 340, and a conductive via 342 a passing through the dielectric layer 340 and electrically conductive to the circuit layer 342 and the second circuit layer 31.

As shown in FIG. 3B, the method further comprises forming on the fourth heat sink 254 and the circuit layer on the external surface of the circuit build-up structure 34 a second solder mask 32, which comprises the openings 320 for exposing the electrically conductive pad 344 and the fourth heat sink 254, allowing a semiconductor chip (not shown) to be disposed on the fourth heat sink 254 and dissipating heat generated by the semiconductor chip in operation via the heat sinks 251 to 254 and the conductive bumps 21. The method further comprises forming a metal protection layer (not shown) such as a nickel/gold layer on the electrically conductive pads 344 in the openings 320 of the second solder mask 32. The method further comprises removing the carrier board 20, so as to form a circuit board structure embedded with heat sinks.

In summary, the circuit board structure and the method for fabricating the same provides a carrier board formed with a plurality of conductive bumps, a first solder mask formed on the carrier board for exposing the conductive bumps, a first circuit layer and a first heat sink formed on the first solder mask and the conductive bumps, a dielectric layer formed on first circuit layer and the first solder mask where neither the first heat sink nor the second heat sink is formed, a second circuit layer formed on the dielectric layer, a second circuit layer electrically conductive by the conductive vias to the first circuit layer, to integrate the heat sinks into the circuit board and decrease the thickness of the circuit board. Therefore, the package structure is compact and is suitable for a modern electronic device.

Moreover, embedded with heat sinks, the circuit board needs not to reserve a certain space for the disposition of the heat sinks and has a larger circuit layout space, so as to overcome the drawback of the prior art that the circuit board does not have a big layer space because a certain space on the circuit board has to be reserved for a heat dissipating spreader ready to be adhered to the circuit board.

Further, in the present invention the heat sinks are integrated into the circuit board to for a circuit board structure having well heat dissipating capability, such that heat dissipated by a semiconductor chip disposed on the heat sinks can be conducted over the heat sinks. A circuit build-up layer can be further formed on the circuit board structure of the present invention, so as to form a multi-layered circuit structure.

The foregoing descriptions of the detailed embodiments are only illustrated to disclose the features and functions of the present invention and not restrictive of the scope of the present invention. It should be understood to those in the art that all modifications and variations according to the spirit and principle in the disclosure of the present invention should fall within the scope of the appended claims. 

1. A method for fabricating a circuit board structure, the method comprising: forming on a carrier board a plurality of conductive bumps and first solder masks filled in gaps between the conductive bumps for exposing the conductive bumps; forming on the first solder masks and the conductive bumps a conductive layer and on the conductive layer a first resistive layer having a plurality of openings for exposing part of the conductive layer; forming in the openings of the first resistive layer a first circuit layer and a first heat sink; forming on the first heat sink, the first resistive layer and the first circuit layer a second resistive layer having a plurality of openings for exposing the first heat sink; forming a second heat sink on the first heat sink exposed to a region outside of the openings of the second resistive layer; removing the second resistive layer, the first resistive layer and the conductive layer covered by the first resistive layer, and forming a dielectric layer on the first circuit layer and the first solder mask where neither the first heat sink nor the second heat sink is formed; and forming on the second heat sink a third heat sink, and forming on the dielectric layer a second circuit layer electrically conductive to the first circuit layer.
 2. The method of claim 1, wherein forming the conductive bumps comprises: forming on the carrier board a resistive layer having a plurality of openings; and forming the conductive bumps in the openings.
 3. The method of claim 2, wherein the forming the conductive bumps further comprises removing the resistive layer.
 4. The method of claim 1, wherein at least one of the conductive bumps comprises one selected from solder tin and metal materials.
 5. The method of claim 1, wherein forming the second circuit layer comprises: forming in the dielectric layer a plurality of vias for exposing the first circuit layer; forming a conductive layer on the dielectric layer, the second heat sink and the vias; forming on the conductive layer a third resistive layer having a plurality of openings; and electroplating and forming in the openings of the third resistive layer the second circuit layer, the conductive vias and the third heat sink, wherein the second circuit layer is electrically conductive by the conductive vias in the dielectric layer to the first circuit layer, and the third heat sink is formed on the second heat sink.
 6. The method of claim 5, wherein forming the second circuit layer further comprises: removing the third resistive layer and the conductive layer covered thereby.
 7. The method of claim 1 further comprising: forming on the second circuit layer a second solder mask having a varieties of openings for exposing the third heat sink and part of the second circuit layer as electrically conductive pads; and removing the carrier board.
 8. The method of claim 7, wherein the electrically conductive pads are covered by a metal protection layer.
 9. The method of claim 1 further comprising: performing a circuit build-up process on the second circuit layer and the third heat sink to form on the second circuit layer a circuit build-up structure and increase a thickness of the heat sink, the circuit build-up structure having an external surface formed with a circuit layer formed with a plurality of electrically conductive pads; forming on the circuit build-up structure and external surfaces of the heat sinks a second solder mask having a plurality of openings for exposing the electrically conductive pads and the heat sinks; and removing the carrier board.
 10. The method of claim 9, wherein the electrically conductive pads having a surface formed with a metal protection layer.
 11. A circuit board structure comprising: a dielectric layer having a first surface and a second surface; a plurality of heat sinks embedded in the dielectric layer and protruding to a region above the second surface of the dielectric layer; a first circuit layer embedded in the dielectric layer and disposed evenly with the first surface of the dielectric layer; and a second circuit layer formed on the second surface of the dielectric layer second surface and electrically conductive to the first circuit layer, wherein the first circuit layer is electrically conductive by a conductive via formed in the dielectric layer to the second circuit layer.
 12. The circuit board structure of claim 11, wherein the heat sinks comprise a third heat sink protruding to a region above the second surface of the dielectric layer, and a first heat sink and a second heat sink, both of which are embedded in the dielectric layer.
 13. The circuit board structure of claim 11 further comprising: a first solder mask covered on the first circuit layer and the first surface of the dielectric layer and having a pluralities of openings for exposing part of the first circuit layer; and a plurality of conductive bumps formed in the openings of the first solder mask.
 14. The circuit board structure of claim 13, wherein at least one of the conductive bumps comprises one selected from the group consisting of solder tin and a metal material.
 15. The circuit board structure of claim 11 further comprising on the second circuit layer, the third heat sink and the second surface of the dielectric layer a second solder mask having a plurality of openings for exposing the third heat sink and part of second circuit layer as a plurality of electrically conductive pads.
 16. The circuit board structure of claim 15 further comprising a metal protection layer formed on the electrically conductive pads.
 17. The circuit board structure of claim 11 further comprising a circuit build-up structure formed on the second circuit layer and the second surface of the dielectric layer second surface, and a heat sink formed on the third heat sink.
 18. The circuit board structure of claim 17 further comprising a solder mask formed on the circuit build-up structure and having a plurality of openings for exposing the electrically conductive pads on a circuit layer on an external surface of the circuit build-up structure.
 19. The circuit board structure of claim 18 further comprising a metal protection layer formed on the electrically conductive pads. 